An elevator typically comprises a hoistway S, an elevator car and a counterweight both vertically movable in the hoistway, and a drive machine M which drives the elevator car under control of an elevator control system. The drive machine typically comprises a motor and a drive wheel engaging an elevator roping, which is connected to the car. Thus, driving force can be transmitted from the motor to the car via the drive wheel and the roping. The roping passes around the drive wheel and suspends the elevator car and the counterweight and comprises a plurality of ropes connecting the elevator car and the counterweight. The roping can be connected to the car and counterweight via diverting wheels. This results in a lifting ratio of 2:1 or greater for these elevator units, depending on via how many diverting wheels the elevator unit in question is suspended. There are several reasons for choosing a high lifting ratio. Importantly, this kind of lifting ratio can be used as a means for increasing the rotational speed of the motor of the drive machine relative to the traveling speed of the car, which is advantageous especially in case of elevators where the drive machine must be dimensioned small in size, or in case of elevators with gearless connection between the motor and drive wheel or in case of elevators with need for reducing torque producing capacity from the motor. It is a common goal in modern elevators to position the drive machine in the top part of the hoistway. By providing said advantages, using the lifting ratio of 2:1 or greater facilitates achieving this goal.
The bending radius of the ropes sets limits for the overall structure of the elevator. For instance the diverting wheels must have a diameter suitable for the ropes. This affects the space efficiency of the elevator and it has been difficult to design an elevator of simple and space efficient structure if the bending radius of the rope is high. For this reason the rope number has been high, and the rope material and structure selected so that a small bending radius can be provided. This effect is relevant especially with elevators having a lifting ratio of 2:1 or higher, because the ropes need to pass around diverting wheels. Thereby, it has been difficult to use ropes which require high bending radius in this type of elevators.
In the elevators of prior art as described above, it is typical to use a roping, which has a great number of metallic load bearing members in the form of twisted steel wires. A roping of this kind has its advantages such as low cost and small bending radius due to twisted structure. However, a metallic roping is heavy and often requires use of a compensation roping to compensate masses of the suspension roping. A drawback of this kind of elevator is therefore that the great rope mass reduces energy efficiency and increases complexity of the elevator construction. The known ropes also have a longitudinal stiffness of a scale that requires use a great number of ropes so as to achieve the desired total load bearing capability, which makes the elevator more complicated.